1. Field of the Invention
The present invention relates to an error correction circuit for correcting an error in a received digital television broadcasting signal.
2. Description of the Related Art
Recent common technology for supplying digital TV broadcasting signals enables commercial digital television broadcasting. Two types of digital television broadcasting are now available, one in which digital TV broadcasting signals are transmitted via a satellite, and one in which such signals are transmitted terrestrially. In the following, satellite digital television broadcasting will be described.
FIG. 3 is a diagram showing a structure of digital data corresponding to one frame to be received by a satellite digital broadcasting receiver, in which each frame of digital data contains 39936 symbols. Here, one symbol refers to the signal or signals received in synchronism with one clock. The head of one frame comprises a TMCC (Transmission Multiplexing Configuration Control) signal and a synchronous word signal, wherein the TMCC signal contains control information concerning a slot signal and a transmission method, and wherein the synchronous word signal contains a total of forty symbols. The TMCC signal and the synchronous word signal together comprise 192 symbols, and both signals are transmitted in the form of a binary phase shift keying modulation signal (BPSK).
Following the TMCC signal and the synchronous word signal, data (video, audio, and so on) and a carrier clock burst signal are alternately arranged. Each data item has 203 symbols, while each carrier clock burst signal has four symbols. The carrier clock burst signal is a BPSK modulation signal.
While data consisting of 203 symbols and TMCC signal or the synchronous word signal consisting of one symbol together make one set, successive 204 symbols are referred to as one slot.
Each slot is modulated using various modulation methods. After being frequency locked (phase locked), a synchronous word is detected for establishment of frame synchronism. Then, the content of a TMCC signal is demodulated to determine the modulation method used to modulate the data to be transmitted, and the order in which the data is to be transmitted. Modulation methods may include 8PSK, QPSK (Quadrature PSK), BPSK, and so on.
FIG. 4 is a diagram showing a structure of a satellite digital broadcasting receiver. A digital television signal sent via a satellite is subjected to synchronism detection in a tuner 61, where frequency down conversion is also applied. Resultant signals I and Q are output from the tuner 61 to an orthogonal phase demodulation circuit 62 for demodulation to thereby generate baseband of the signals I and Q. Thereafter, PSK demodulation circuit 63 applies various PSK demodulation to the signals I and Q to thereby produce a PSK demodulated signal. The PSK demodulated signal is given error correction in an error correction circuit 64. An error-corrected PSK demodulated signal is decoded into motion picture data and/or audio data using MPEG (Motion Picture Experts Group) 1 and/or MPEG 2 method in a signal processing circuit 65.
Here, a conventional error correction circuit comprises paths dedicated respectively to data containing a video signal and an audio signal (hereinafter referred to as a main signal), and to a TMCC signal, and conducts error correction in the respective paths. In satellite digital television broadcasting, which employs Reed Solomon Codes, a transmitter side applies Reed Solomon Coding by imparting an error detection redundancy signal to a main signal and a TMCC signal, while a receiver side processes the coded main and TMCC signals using the redundancy signal to determine for correction an error position in the respective signals.
However, conventional provision of an error correction circuit for every signal strain necessitates two error correction circuits. Moreover, use of separate Reed Solomon demodulation circuits for a main signal and a TMCC signal by each error correction circuit results in wasteful circuit structure, and integration of these circuits onto a semiconductor substrate results in a large scale circuit.